PXTA v0.2.0

• pxta check: audit a site, or judge a saved findings.json, and exit 1
  when it breaks the rules. Exit codes 0, 1, 2 (usage or rules file),
  3 (audit could not run), 130.
• Rules file (JSON): fail_on severity, fail_codes, tracker allow and
  block lists, require_banner, and allow exceptions with a required
  reason and an optional until date. Defaults fail on medium and above and
  on banner-not-handled.
• Output as text, GitHub Actions annotations (--format github) and a
  Markdown summary (--summary), plus check.json in the report folder.
• --redact on audit and check: personal values replaced by REDACTED in
  every report file, in every encoding PXTA reads, with a scan of the written
  files that fails the run, and removes the report and working files, if one
  is left. PXTA's own probe values stay.
• With --format github, annotations, the job summary and the log describe
  each problem from its code, tracker, page path and pass and never quote
  captured data, since anyone who can see the run reads them.
• GitHub Action (uses: softdevstudio/pxta@v0.2.0), described in ACTION.md.
  It runs the pxta release it is pinned to and uploads only the report files.
  Tested on Linux and macOS runners with real audits, and on Windows with
  saved findings.
• New problem codes in check results: tracker-not-allowed,
  tracker-blocked, no-banner. Finding codes are unchanged.